python - 从特定键开始迭代有序的字典项

Question

问题是在 python 2.7 中设计的。

我正在使用 OrderedDict 来存储一些项目，如下所示:

d = OrderedDict(zip(['a', 'b', 'c', 'd'], range(4)))

(d 等于 {'a': 0, 'b': 1, 'c': 2, 'd': 3})

有没有办法从特定的键开始迭代字典d？ 例如，我想从键 'b'

开始迭代 d 项

非常感谢!

Answer 1

适用于 Python 2 和 3 的解决方案，使用 itertools.dropwhile():

from __future__ import print_function

from collections import OrderedDict
from itertools import dropwhile

d = OrderedDict(zip(['a', 'b', 'c', 'd'], range(4)))

for k, v in dropwhile(lambda x: x[0] != 'b', d.items()):
    print(k, v)

输出:

b 1
c 2
d 3

Python 2，避免使用 .items()::

创建键值列表

for k, v in dropwhile(lambda x: x[0] != 'b', d.iteritems()):
    print(k, v)

时机

%timeit
for each in d.items()[d.keys().index('b'):]:
    pass
The slowest run took 5.18 times longer than the fastest. This could mean that an intermediate result is being cached.
100000 loops, best of 3: 3.27 µs per loop

%%timeit
for each in islice(d.iteritems(), d.keys().index('b'), None):
    pass
The slowest run took 5.23 times longer than the fastest. This could mean that an intermediate result is being cached.
100000 loops, best of 3: 3.05 µs per loop

%%timeit
for k, v in dropwhile(lambda x: x[0] != 'b', d.iteritems()):
    pass
The slowest run took 4.92 times longer than the fastest. This could mean that an intermediate result is being cached.
100000 loops, best of 3: 2.23 µs per loop